1. Field of the Invention
The present invention relates to a surface emitting laser and a method of manufacturing the surface emitting laser, and more particularly, to a surface emitting laser for realizing higher power and improved quantum efficiency with a fundamental transverse mode and a method of manufacturing the surface emitting laser.
2. Description of the Related Art
A conventional vertical cavity surface emitting laser (hereinafter, referred to as VCSEL) employs a structure in which the diameter of a light emitting region is narrowed to approximately 5 μm in order to obtain laser oscillation of a fundamental transverse mode.
Therefore, the volume of an active layer region becomes smaller, thereby reducing the optical power.
In order to solve this problem, a surface emitting semiconductor laser in which higher-order transverse mode oscillations are suppressed without affecting the fundamental transverse mode oscillation is proposed in Japanese Patent Application Laid-Open No. 2002-208755.
FIG. 5 shows a surface emitting semiconductor laser in which a lower n-type distributed Bragg reflector (DBR) layer 103, an active region 104, and an upper p-type DBR layer 106 are provided above a semiconductor substrate 101.
An upper p-type electrode 108 having an aperture portion 127 serving as a laser light output region is formed above the upper p-type DBR layer 106. A current confinement region 124 is formed as an oxidized region.
According to the surface emitting semiconductor laser having the structure described above, the aperture diameter of the current confinement region 124 and the aperture diameter of the upper p-type electrode 108 are determined based on the reflectance of a cavity corresponding to the upper p-type electrode 108 such that the optical loss difference of the cavity between the higher-order transverse mode and the fundamental transverse mode of laser light becomes larger.
That is, the aperture diameter of the current confinement region which is provided in the vicinity of the active layer (active region) and inserted to limit a current path and the aperture diameter of the upper p-type electrode provided to output laser light are determined as described above. Therefore, high optical power is achieved in the fundamental transverse mode.
In a light emitting device having a mesa structure, a current confinement region provided in the vicinity of an active layer is greatly effective to reduce a leak current flowing through a processed surface of the mesa structure. Therefore, the current confinement region is extremely important for a high-efficiency mesa type VCSEL.
On the other hand, laser oscillation depends not only on reflection characteristics of a cavity but also on light emission recombination (gain) distribution of the active layer.
In particular, in the current confinement region having an aperture portion for limiting a path for current (for confining current) to be injected to the active layer by an oxidized region, the current is confined to the aperture portion. However, the current concentrates on a peripheral region of the aperture portion, so the gain necessarily becomes larger, thereby exciting the higher-order transverse mode. Therefore, in the structure in which the reflection loss of the cavity is controlled to realize the fundamental transverse mode oscillation as disclosed in Japanese Patent Application Laid-Open No. 2002-208755, the gain in the higher-order transverse mode increases as described above, so the reflection loss of the cavity increases to suppress the higher-order transverse mode.
Thus, the conventional example as described above has a problem in conversion efficiency (quantum efficiency) between injection power and optical power.
In addition, the conventional example has a problem in that, a difference between a refractive index of the oxidized region of the current confinement region and a refractive index of a non-oxidized region is large, so the light emitting device becomes a refractive index waveguide type in which waveguide light is strongly confined and has a waveguide structure in which the higher-order transverse mode is easily obtained.